The attached .atr file is the unreleased, unfinished Star Raiders II game for the Atari 8-bit computers, created by Aric Wilmunder in 1983 when he worked for Atari coin-op. Use with an Atari emulator or on real hardware.
Also attached: guide to controls in the game and "The Authoritative Star Raiders II", Aric's description of why the game was created.
Jan 16 2016: The source code and original design document have been recovered and uploaded here as .ATR files. I have also converted the design document and program notes to pretty formatted PDFs and uploaded them as well.